Improve diagnostics when the parser encounters a declarator with an

unknown type name, e.g.,

  foo::bar x;

when "bar" does not refer to a type in "foo". 

With this change, the parser now calls into the action to perform
diagnostics and can try to recover by substituting in an appropriate
type. For example, this allows us to easily diagnose some missing
"typename" specifiers, which we now do:

  test/SemaCXX/unknown-type-name.cpp:29:1: error: missing 'typename'
        prior to dependent type name 'A<T>::type'
  A<T>::type A<T>::f() { return type(); }
  ^~~~~~~~~~
  typename 

Fixes PR3990.

llvm-svn: 84053

1 files changed, 29 insertions, 6 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index e15a4cd6880..b56c33170cb 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -688,13 +688,36 @@ bool Parser::ParseImplicitInt(DeclSpec &DS, CXXScopeSpec *SS,
     }
   }
 
-  // Since this is almost certainly an invalid type name, emit a
-  // diagnostic that says it, eat the token, and mark the declspec as
-  // invalid.
-  SourceRange R;
-  if (SS) R = SS->getRange();
+  // This is almost certainly an invalid type name. Let the action emit a 
+  // diagnostic and attempt to recover.
+  Action::TypeTy *T = 0;
+  if (Actions.DiagnoseUnknownTypeName(*Tok.getIdentifierInfo(), Loc,
+                                      CurScope, SS, T)) {
+    // The action emitted a diagnostic, so we don't have to.
+    if (T) {
+      // The action has suggested that the type T could be used. Set that as
+      // the type in the declaration specifiers, consume the would-be type
+      // name token, and we're done.
+      const char *PrevSpec;
+      unsigned DiagID;
+      DS.SetTypeSpecType(DeclSpec::TST_typename, Loc, PrevSpec, DiagID, T, 
+                         false);
+      DS.SetRangeEnd(Tok.getLocation());
+      ConsumeToken();
+      
+      // There may be other declaration specifiers after this.
+      return true;
+    }
+    
+    // Fall through; the action had no suggestion for us.
+  } else {
+    // The action did not emit a diagnostic, so emit one now.
+    SourceRange R;
+    if (SS) R = SS->getRange();
+    Diag(Loc, diag::err_unknown_typename) << Tok.getIdentifierInfo() << R;
+  }
 
-  Diag(Loc, diag::err_unknown_typename) << Tok.getIdentifierInfo() << R;
+  // Mark this as an error.
   const char *PrevSpec;
   unsigned DiagID;
   DS.SetTypeSpecType(DeclSpec::TST_error, Loc, PrevSpec, DiagID);